Method and apparatus to prevent stent damage caused by laser cutting

ABSTRACT

Apparatus, method and system for cutting a polymeric stent including the use of a polymeric mandrel as a laser shielding device. The polymeric mandrel is allowed to roll freely within a polymeric tube that is cut into a polymeric stent.

FIELD OF THE INVENTION

The present invention relates to stents; more particularly, thisinvention relates to processes for making a polymer-based stent.

BACKGROUND OF THE INVENTION

The invention relates to radially expandable endoprostheses which areadapted to be implanted in a lumen of a tubular organ. An“endoprosthesis”, or stent, corresponds to an artificial implantablemedical device that is placed inside the body. A “lumen” refers to acavity of a tubular organ such as a blood vessel. A stent is an exampleof these endoprostheses. Stents are generally cylindrically shapeddevices which function to hold open and sometimes expand a segment of ablood vessel or other anatomical lumens such as urinary tracts and bileducts. Stents are often used in the treatment of atheroscleroticstenosis in blood vessels. “Stenosis” refers to a narrowing orconstriction of the diameter of a bodily passage or orifice. In suchtreatments, stents reinforce vessels and prevent restenosis followingangioplasty in the vascular system. “Restenosis” refers to thereoccurrence of stenosis in a blood vessel or heart valve after it hasbeen treated (as by balloon angioplasty or valvuloplasty) with apparentsuccess.

A treatment involving a stent includes both delivery and deployment ofthe stent. “Delivery” refers to introducing and transporting the stentthrough a lumen of a tubular organ to a region requiring treatment.“Deployment” corresponds to the expanding of the stent within the lumenat the treatment region. Delivery and deployment of a stent may beaccomplished by positioning the stent about one end of a catheter,inserting the end of the catheter through the skin into the lumen,advancing the catheter in the lumen to a desired treatment location,expanding the stent at the treatment location, and then removing thecatheter from the lumen. In the case of a balloon expandable stent, thestent is mounted about a balloon disposed on the catheter. Mounting thestent typically involves compressing or crimping the stent onto theballoon. The stent is then expanded by inflating the balloon. Theballoon may then be deflated and the catheter withdrawn. In the case ofa self-expanding stent, the stent may be secured to the catheter via aretractable sheath or a sock. When the stent is in a desired bodilylocation, the sheath may be withdrawn allowing the stent to self-expand.

Stents have been made of many materials including metals and polymers.Polymer materials include both nonbioerodable and bioerodable plasticmaterials. In some applications, a polymeric bioerodable stent may bemore advantageous than a metal stent due to its biodegradeability andincreased flexibility relative to the metal stent. The cylindricalstructure of a stent is typically composed of a scaffolding thatincludes a pattern or network of interconnecting structural elements orstruts. The scaffolding can be formed from wires, tubes, or planar filmsof material rolled into a cylindrical shape. In addition, a medicatedstent may be fabricated by coating the surface of either a metallic orpolymeric scaffolding with a polymeric carrier. The polymeric carriercan include an active agent or drug. Furthermore, the pattern that makesup the stent allows the stent to be radially expandable andlongitudinally flexible. Longitudinal flexibility facilitates deliveryof the stent and rigidity is needed to hold open a lumen of a tubularorgan. Generally, the pattern should be designed to maintain thelongitudinal flexibility and rigidity required of the stent. The stentshould also have adequate strength in the circumferential direction.

A number of techniques have been suggested for the fabrication of stentsfrom tubes and planar films or sheets. One such technique involves lasercutting or etching a pattern onto a material. Laser cutting may beperformed on a planar film of a material which is then rolled into atube. Alternatively, a desired pattern may be etched directly onto atube. Other techniques involve cutting a desired pattern into a sheet ora tube via chemical etching or electrical discharge machining. Lasercutting of stents has been described in a number of publicationsincluding U.S. Pat. No. 5,780,807 to Saunders, U.S. Pat. No. 5,922,005to Richter and U.S. Pat. No. 5,906,759 to Richter.

In a typical method of manufacturing a metal stent with a laser, amandrel is placed inside the lumen of metal tubing. A “mandrel” refersto a metal bar or rod on which an implantable medical device may beshaped. The mandrel provides structural support to the tubing as it isbeing cut and shaped. See, e.g., U.S. Pat. No. 5,780,807 to Saunders.After a stent has been cut, the support on at least one end must beremoved to allow removal of the stent. A new piece of tubing is thenattached and must be realigned and re-supported. Therefore, there is aneed for a stent cutting device that allows removal of completed stentsfrom the apparatus and allows for the cutting of more stents from theremaining tubing without the inherent efficiencies of readjusting thesupport means for the removal of each stent.

SUMMARY OF THE INVENTION

The invention is directed to methods, systems, and apparatuses formanufacturing polymeric stents.

One aspect of the present invention is directed to a method of producinga polymeric stent including supporting a tubular polymeric member on atleast one end and providing a polymeric mandrel within the tubularmember. The polymeric mandrel freely rolls in the tubular member andprevents a laser from damaging the opposite side of the tubular memberfrom the side that is being cut. The apparatus also includes apressurized gas jet to force debris generated during the laser processout of the end of the tubing. In some embodiments, both sides of thetubular polymeric member are supported.

An additional aspect of the present invention is directed to anapparatus for producing a polymeric stent. The apparatus includes asupport for at least one end of a tubular polymeric member and also apolymeric mandrel within the tubular member. The polymeric mandrelfreely rolls in the tubular member and prevents a laser from damagingthe opposite side of the tubular member from the side that is being cut.The apparatus also includes a pressurized gas jet to force debrisgenerated during the laser process out of the end of the tubing. In someembodiments, both sides of the tubular polymeric member are supported.

Another aspect of the present invention is directed to a system forproducing a polymeric stent using the apparatuses and methods of thepresent invention. The system includes providing an apparatus forsupporting a tubular polymeric member on at least one end and having apolymeric mandrel within the tubular member. The polymeric mandrelfreely rolls in the tubular member and prevents a laser from damagingthe opposite side of the tubular member from the side that is being cut.The apparatus also includes a pressurized gas jet to force debrisgenerated during the laser process out of the end of the tubing. In someembodiments, both sides of the tubular polymeric member are supported.After the tubular polymeric member is cut into a stent, the finishedstent may be separated from the rest of the tubular polymeric member sothat a second stent may be cut without readjusting the support(s),thereby increasing the efficiency of the process.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference, and as if eachsaid individual publication or patent application was fully set forth,including any figures, herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a polymeric stent manufacturing device used in oneform of a method for manufacturing a polymeric stent.

FIG. 2 shows an enlarged view of a polymeric stent manufactured by thestent manufacturing device in FIG. 1.

FIG. 3 is a cross-sectional view of a polymeric stent of FIG. 2manufactured using inadequate protection from the laser cutter.

FIG. 4 is an enlarged view of a portion of a distal ring of thepolymeric stent of FIG. 2 manufactured using inadequate protection fromthe laser cutter.

FIG. 5 illustrates an embodiment of a polymeric stent manufacturingdevice used in one form of a method of the present invention.

FIG. 6A is an end view of the embodiment of the device in FIG. 5.

FIG. 6B is a radial view of the polymeric stent and polymeric mandrel ofthe present invention.

FIG. 7A illustrates an embodiment of a polymeric stent manufacturingdevice used in the present invention.

FIG. 7B illustrates another embodiment of a polymeric stentmanufacturing device used in the present invention.

FIG. 7C illustrates an end view of the embodiment of the device in FIGS.7A, 7B.

FIG. 8A illustrates a further embodiment of a polymeric stentmanufacturing device used in the present invention.

FIG. 8B illustrates an embodiment of a polymeric stent manufacturingdevice used in the present invention.

FIG. 8C illustrates an end view of an embodiment of the device in FIGS.8A, 8B.

FIG. 8D illustrates an end view of an embodiment of the device in FIGS.8A, 8B.

FIG. 9 shows an enlarged view of a polymeric stent manufactured by thestent manufacturing device of the present invention.

FIG. 10 is a cross-sectional view of the polymeric stent of FIG. 9.

FIG. 11 is an enlarged view of a portion of a distal ring of thepolymeric stent of FIG. 9.

DETAILED DESCRIPTION OF EMBODIMENTS

In a conventional lasing process of manufacturing a polymeric stent froma tube, a mandrel may not typically be employed. Due to the retentivenature of polymeric materials for foreign particulates, a glass or metalmandrel may contaminate the polymeric stent if a laser beam from thelaser strikes it and releases such contaminates. The glass or metaldebris can not be cleaned from the surface of the polymer stent usingconventional techniques commonly employed for metal stents, such aselectropolishing due to the sensitivity of the polymer stent toaggressive chemicals and heat treatments. In other words, a glassmandrel may leave glass particulates, and a metal mandrel may leavelarge amounts of metal oxide contamination melted into the inner surfaceof the polymer stent, respectively. Such contaminants may cause adverseeffects during and/or after the stent is implanted into the lumen of abodily organ, including the increased mortality rate of mammals duringpreclinical trials due to glass contamination. The increased mortalityis due to the thrombus formation caused by the interaction of blood withthe glass debris. The glass debris causes a very strong thromboticresponse, which may lead to vessel occlusion and death.

However, non-use of a mandrel in the manufacturing process of apolymeric stent, may cause problems aside from contamination through useof glass or metal mandrels. It has been observed that in the manufactureof polymeric stents, damage to the inner surface of the stent can occur.The damage is typically in the form of at least one angled cut, or“nick”, within the inner surface area. The angled cuts are the result ofthe laser beam reaching the inner surface as the equal-but-oppositeouter surface is being lased. The damage caused thereby may causeproblems with delivery of the stent and/or adverse body reactions. Thisproblem may be remedied by use of a typical mandrel (which may provide ashielding effect) in the manufacturing process; however, the problemsassociated with the use of metal or glass mandrels as describedpreviously may result. Additional damage that is not readily apparentmay also be caused. The impact of an unfocused laser beam on theopposite side of the tube may cause molecular weight loss that is notreadily detectable. This may result in a change in the mechanicalproperties of the stent in an unpredictable manner.

FIG. 1 illustrates a polymeric stent manufacturing device 30 related tothe manufacturing process of a polymeric stent. Device 30 for supportinga polymeric tube 8 includes a support member 32 and a lock member 36.Support member 32 may connect to a motor 38A to provide rotationalmotion about the longitudinal axis of a stent (depicted by arrow 40).Another motor 38B may also be provided for moving device 30 in a backand forth linear direction along rail 42. Polymeric stent manufacturingdevice 30 may be in fluid communication with a vacuum device 44 forcollecting excess polymeric material. Lock member 36 may be coupled tothe vacuum device 44 via a conduit 46. A coupler 48 allows device 30 torotate with respect to conduit 46 and vacuum 44. A mandrel 34 isattached between support member 32 and lock member 36. The outerdiameter of mandrel 34 will typically be smaller than the inner diameterof polymeric tube 8, as positioned on fixture 30, so as to prevent theouter surface of mandrel 34 from making contact with the inner surfaceof polymeric tube 8. Support member 32 and lock member 36 includeconical end portions 56A and 56B, instead of flat ends, for penetratinginto ends of polymeric tube 8. The end portions 56A and 56B can taperinwardly at an angle of about 15 degrees to about 75 degrees, morenarrowly from about 30 degrees to about 60 degrees. By way of example,angle θ can be about 45 degrees. If the outer diameter of the mandrel isin contact with the inner diameter of the tube from which the stent iscut then there is a very strong probability that the inner mandrel willbe welded to the stent.

In the manufacturing process, a polymeric tube 8 may be placed over themandrel 34 between support member 32 and lock member 36. The wallthickness of the polymeric tube 8 will typically vary throughout thetube body due to variations in the manufacturing process of polymerictubes. A coaxial gas jet, rotary collet, tube support and beaming blockapparatus of a laser (from hereonout abbreviated as a laser 100) maythen be used for the etching process to form a polymeric stent 10′ fromthe polymeric tube 8. The laser 100 can include a laser beam 102, afocusing lens 104, a gas input 106, a coaxial gas jet assay 108 and agas jet 110. A resultant polymeric stent 10′ manufactured using device30 is illustrated in FIG. 2. Polymeric stent 10′ includes a plurality ofstruts 12′ linked by connecting elements 14′ with gaps 16′ positioned inbetween struts 12′ and connecting elements 14′. The polymeric stent 10′can include a proximal ring 18′, a distal ring 20′ and at least onecentral ring 22′.

FIG. 3 is a cross-section of the polymeric stent 10′ of FIG. 2 if it ismanufactured without using a protective mandrel or with a mandrel ofincorrect thickness. As shown, the stent 10′ includes an inner surface26′ and an outer surface 24′. The inner surface 26′ of the stent 10′ mayhave at least one “nick” or angled cut 28 when manufactured using thedevice 30 without an adequate mandrel. In FIG. 4, an enlarged view of aportion of the distal ring 20′ is depicted. In this view, at least oneangled cut 28 on the inner surface 26′ can be seen more clearly. Itshould be understood that the angled cuts 28 may occur throughout theinner surface 26′ of the stent 10′.

The manufacturing process as discussed in connection with FIG. 1 hasseveral drawbacks. First, the process may lead to the manifestation ofangled cuts 28. For example, if the mandrel is too thick, the laserpower may be diverted to a different portion of the polymeric tube 8,contributing to the manifestation of angled cuts 28. After the laserenters the polymeric tube 8, its power decreases as it gets further fromthe surface. If the beam encounters a mandrel soon after entering thepolymeric tube 8, then the energy may not have dissipated very much andthe beam may be deflected to a nearer inner surface with more energy,thereby contributing to angled cuts 28. In addition, the inherentvarying wall thickness of the polymeric tubes may contribute to themanifestation of angled cuts 28. As an illustration, the power of thelaser 100 may be adjusted to etch a first portion of the polymeric tube8 with a first thickness. However, this same power may be too strong forthe etching of a second portion of polymeric tube 8 with a secondthickness. As a result, although appropriate for the first portion ofpolymeric tube 8 with the first thickness, the same power of the laser100 for the second portion of the polymer tube 8 with the secondthickness may be too strong and therefore cause the manifestation ofangled cuts 28. The typical wall thickness of a tube from which a stentis cut is 0.006″+/−0.001″, which may lead to the variation discussedabove.

A second drawback to the manufacturing process in FIG. 1 is a resultingrough inner surface of polymeric tube 8 due to the inability to clearaway debris from the cutting area. This may result in heat buildup thatis undesired in certain areas of the stent. Additionally, rough surfacescan cause an increase in protein accumulation leading to a thrombogenicresponse. The present invention solves the problem by polishing theinside surface of polymeric tube 8 while the tube is being cut into astent.

A third drawback to the manufacturing process in FIG. 1 is the inabilityto cut more than one stent without having to move and reposition supportmember 32 and lock member 36 for each new stent.

In FIGS. 5 through 9, embodiments of a polymeric stent manufacturingdevice 50, 70, 80 related to a manufacturing process of the presentinvention are illustrated. In FIG. 5, device 50 for supporting apolymeric tube 58 can include a first support member 52 at first end 55of polymeric tube 58, a polymeric mandrel 54, and a second supportmember 51 at the second end 56 of polymeric tube 58. Support member 52may contain a motor to provide rotational motion about the longitudinalaxis A of a stent. The types and specifications of the various motorswhich can be used in any of the embodiments herein would be apparent tothose skilled in the art. The term stent is broadly intended to includeself- and balloon-type as well stent-grafts.

Polymeric mandrel 54 is allowed to freely roll around the insidediameter of polymeric tube 58. In some embodiments, polymeric mandrel 54is not supported specifically at either end, but supported along itsentire length by polymeric tube 58. Polymeric mandrel 54 may be hollowor solid and made from the same or different polymer(s) as polymerictube 58. In an embodiment as shown in FIG. 6B, polymeric mandrel 64 withan outside diameter of OD_(M) is positioned longitudinally withinpolymeric tube 68 of inside diameter ID_(T) such that it is in contactwith approximately the bottom of polymeric tube 68. As polymeric tube 68is rotated in direction D_(T), polymeric mandrel will roll in directionD_(M). Freely roll is understood to mean the travel of polymeric mandrel64 in reaction to the angular force applied by rolling polymeric tube68. In an embodiment, friction F at the contact point between polymericmandrel 64 and polymer tube 68, and gravity G are the major externalforces applied to polymeric mandrel 64. If friction F is not too high,polymeric mandrel 64 will smoothly roll to a new position near thebottom of polymeric tube 68. If friction F is high, or there areimperfections like bumps on the inside surface of polymeric tube 68, oron the surface of polymeric mandrel 64, then polymeric mandrel 64 mayhave a bouncy, irregular, motion. Friction F may be increased byroughening the surface of polymeric mandrel 64 or roughening the insidesurface of polymeric tube 68. In an embodiment, polishing of the insidesurface of polymeric tube 68 may occur using a rough polymeric mandrel64. In another embodiment, a smooth polymeric mandrel 64 may be used topolish the inner surface of polymeric tube 68.

Polymeric stent manufacturing device 50 is positioned under a lasercutter 100 for cutting polymeric tube 58. An optional nozzle 57 providespressurized gas to the surface of polymeric tube 58 near the lasercutting site. Nozzle 57 is positioned relative to the outside surface ofpolymeric tube 58 at an angle θ of about 15 degrees to about 75 degrees,more narrowly from about 30 degrees to about 60 degrees. By way ofexample, angle θ can be about 45 degrees.

The pressurized gas can be any gas including air or inert gases such asnitrogen, helium, and argon. In an embodiment the gas is helium. The gasaids in forcing debris out of a laser cut kerf in direction 59 towardthe second end of polymeric tube 58. In another embodiment, the gas iscool, facilitating in cooling the generally tubular polymeric tube 58and/or polymeric mandrel 54. In some embodiments, the gas temperature isambient, less than ambient, or greater than ambient. In one embodimentthe pressurized gas temperature is supplied between about 0° C. andabout 25° C. The flowrate of the gas may range from about 2 SCFH toabout 10 SCFH. The assist gas will also influence the nature of theplasma formed during the cutting process.

FIG. 6A is a cross-sectional end view of the apparatus in FIG. 5 showingpolymeric tube 68 with polymeric mandrel 64 protecting the insidesurface of polymeric tube 68 opposite laser 100 from the cutting beam.Beam 101 passes through a space between the inner tube surface ofgenerally tubular polymeric member 68 and the outer surface of polymericmandrel 64 and contacts polymeric mandrel 64 such that the laser beam isprevented from contacting the portion of the inner tube surface 69 uponwhich polymeric mandrel 64 is placed.

FIGS. 7A, 7B and 7C illustrate several embodiments of the apparatusesand methods for cutting a stent according to the present invention. Agenerally tubular polymeric member 78 having a working outer tube 78 Oand an inner tube surface 78 I defining an inside diameter 78 ID andhaving a first end 75 and a second end 76, has its first end 75 mountedon support 72 and its second end 76 mounted on second support 71. Apolymeric mandrel 74 having an outer surface 74 O defining an outerdiameter 740D that is smaller than the inside diameter of generallytubular polymeric member 78 is placed within generally tubular polymericmember 78. Apparatus 70 is placed in operative association with laserbeam 100 which impinges upon the working outer tube surface therebycausing the laser beam 100 to cut a kerf. The beam then passes through aspace between the inner tube surface 78 I of generally tubular polymericmember 78 and the outer surface 74 O of polymeric mandrel 74 andcontacts polymeric mandrel 74 such that the laser beam 100 is preventedfrom contacting the area of the inner tube surface 79 upon whichpolymeric mandrel 74 is placed and shields. Optionally, pressurized gasis dispensed through a nozzle 77 near the laser beam cutting point,thereby forming a jet of pressurized gas to force debris out of thelaser cut kerf in direction 79 toward the second end 76 of generallytubular polymeric member 78. A stent pattern is cut in generally tubularpolymeric member 78 near the second end 76 and the completed stent 73 isremoved from the second end 76 of generally tubular polymeric member 78by sliding stent 73 onto second support 71. In FIG. 7A, the new secondend 76′ of generally tubular polymeric member 78 is not supported bysecond support 71 after the first stent 73 has been removed. A secondstent may now be cut from the remaining portion of generally tubularpolymeric member 78 near new second end 76′.

In one embodiment as illustrated in FIG. 7B, generally tubular polymericmember 78 may continue to be supported at the new second end 76′ bysecond support 71 after the first stent 73 has been removed. This may beaccomplished by moving second support 71 into the new second end 76′ ofthe remaining portion of generally tubular polymeric member 78 whilestent 73 is still on second support 71. Polymeric mandrel 74 may also bemoved toward support 72 to accommodate second support 71.

FIGS. 8A and 8B illustrate several embodiments of the apparatuses andmethods for cutting a stent according to the present invention. Agenerally tubular polymeric member 88 having a working outer tube 88 Oand an inner tube surface 88 I defining an inside diameter 88 ID andhaving a first end 85 and second end 86, has its first end 85 mounted onsupport 82 and its second end 86 left unsupported. A polymeric mandrel84 having an outer surface 84 O defining an outer diameter 840D that issmaller than the inside diameter 88 ID of generally tubular polymericmember 88 is placed within generally tubular polymeric member 88.Apparatus 80 is placed in operative association with laser beam 100which impinges upon the working outer tube surface thereby causing thelaser beam 100 to cut a kerf. The beam then passes through a spacebetween the inner tube surface 88 I of generally tubular polymericmember 88 and the outer surface 84 O of polymeric mandrel 84 andcontacts polymeric mandrel 84 such that the laser beam 100 is preventedfrom contacting the area of the inner tube surface 89 upon whichpolymeric mandrel 84 is placed and shields. Pressurized gas is dispensedthrough a nozzle 87 near the laser beam cutting point, thereby forming ajet of pressurized gas to force debris out of the laser cut kerf indirection 89 toward the second end 86 of generally tubular polymericmember 88. A stent pattern is cut in generally tubular polymeric member88 near the second end 86 and the completed stent 83 is removed from thesecond end 86 of generally tubular polymeric member 88 leaving newsecond end 86′ of generally tubular polymeric member 88. FIG. 8A showsthe apparatus 80 before cutting of generally tubular polymeric member 88has begun. FIG. 8B illustrates the apparatus 80 after a first stent 83has been cut and removed. A second stent may now be cut from theremaining portion of generally tubular polymeric member 88 near newsecond end 86′. In one embodiment, completed stent 83 is removed bysliding completed stent 83 off of polymeric mandrel 84.

A polymeric mandrel is a mandrel made wholly or in part from at leastone type of polymer or a combination of polymers, such as polymer blendsor various types of copolymers. The polymeric mandrel can also be amandrel that is coated with at least one type of polymer or acombination of polymers. The polymeric mandrel can be made from orcoated with a biostable polymer or a bioerodable, biodegradable orbioabsorbable polymer. Bioerodable, biodegradable or bioabsorbable areintended to be used interchangeably unless otherwise indicated. In someembodiments, the polymer is the same as a polymer used to make thestent. In some embodiments, the polymer can be different, so long as thepolymer is biocompatible.

In one embodiment, the polymeric tube and the stent made from the tubecan be made entirely of a polymer or polymers. In an embodiment, thepolymeric mandrel can be made entirely of a polymer or polymers.

Representative examples of biocompatible polymers that can be used forthe polymeric mandrel include, but are not limited to, fluorinatedpolymers or copolymers such as poly(vinylidene fluoride),poly(vinylidene fluoride-co-hexafluoro propene),poly(tetrafluoroethylene), and expanded poly(tetrafluoroethylene);poly(sulfone); poly(N-vinyl pyrrolidone); poly(aminocarbonates);poly(iminocarbonates); poly(anhydride-co-imides), poly(hydroxyvalerate);poly(L-lactic acid); poly(L-lactide); poly(caprolactones);poly(lactide-co-glycolide); poly(hydroxybutyrates);poly(hydroxybutyrate-co-valerate); poly(dioxanones); poly(orthoesters);poly(anhydrides); poly(glycolic acid); poly(glycolide); poly(D,L-lacticacid); poly(D,L-lactide); poly(glycolic acid-co-trimethylene carbonate);poly(phosphoesters); poly(phosphoester urethane); poly(trimethylenecarbonate); poly(iminocarbonate); poly(ethylene); and any derivatives,analogs, homologues, congeners, salts, copolymers and combinationsthereof.

In an embodiment, the polymeric tube and stent can be made from randomand block copolymers of the polymers below, in particular,poly(L-lactide-co-glycolide) (PLGA). The polymeric tube and stent can bemade from PLGA including any molar ratio of L-lactide (LLA) to glycolide(GA). In particular, the polymeric tube and stent can be made from PLGAwith a molar ratio of (LA:GA) including 85:15 (or a range of 82:18 to88:12), 95:5 (or a range of 93:7 to 97:3), or commercially availablePLGA products identified as having these molar ratios. Table 1 providesproperties of some of the above-mentioned polymers. High strength,semicrystalline polymers with a Tg above body temperature include PLLA,PGA, and PLGA. High fracture toughness polymers include PCL, PTMC, PDO,PHB, and PBS. In some embodiments the polymeric tube and the stent aremade entirely of PLLA.

TABLE 1 Properties of biodegradable polymers. Glass- Tensile TransitionModulus Strength Elongation Degradation Polymer Temp (° C.)¹ (Gpa) (Mpa)at break (%) Time (months)^(a) PGA 35-40 7.0¹ 60-80² 30⁴  6-12^(1,2)5-7² PLLA 60-65 2.7¹ 60-70²  3⁴ >24¹ 3²  >36² PDLLA 55-60 1.9¹  2² N/A12-16¹ 2²  12-15² PCL (−65)-(−60)   0.4^(1,2) 20-25² 800-1000⁴ >24¹  0.386⁴  4⁴ >36² PDO (−10)-0       1.5^(1,2) 30² 35³  6-12¹  6² PHB N/A4⁴  40⁴  6⁴ PGA-TMC N/A 2.4¹ N/A N/A  6-12¹ 85/15  50-55¹ 2.0¹ N/A N/A5-6¹ PLGA 75/25  50-55¹ 2.0¹ N/A N/A 4-5¹ PLGA 65/35  45-50¹ 2.0¹ N/AN/A 3-4¹ PLGA 50/50  45-50¹ 2.0¹ N/A N/A 1-2¹ PLGA ¹Medical Plastics andBiomaterials Magazine, March 1998. ²Medical Device Manufacturing &Technology 2005. ³The Biomedical Engineering Handbook, Joseph D.Bronzino, Ed. CRC Press in Cooperation with IEEE Press, Boca Raton, FL,1995. ⁴Science, Vol. 297 p. 803 (2002) ^(a)Degradation time also dependson part geometry.

In various embodiments, the generally tubular polymeric member, alsoreferred to as a working tube, may be made of a different polymer orcopolymer than the polymeric mandrel tube. In one embodiment, theworking tube may be a pure polymer and the mandrel is a copolymer. Forexample, the working tube may be pure PLLA and the mandrel tube may bePLGA with a molar ratio of (LA:GA) including 85:15 or 95:5. In anotherexample, the working tube is a pure polymer and the mandrel is a blend.For example, the mandrel tube can contain >50%, >70%, or >90% of thesame polymer as the working tube. In one example, the working tube isPLLA and the mandrel tube is a blend with 60% PLLA and 40% PLGA (85:15).

Further embodiments of the invention include a working tube made of acopolymer and the mantel tube made of a copolymer. For example, both theworking tube and the mandrel tube may be PLGA with a molar ratio of(LA:GA) including 85:15 or 95:5.

Utilizing the same or very similar tubing stock to make both the workingtube and the mandrel tube has several advantages. First, differentbatches of tube stock can have different monomer and/or low molecularweight species content as contaminants, all of which can affect thedegradation rate of the completed stent. Even a small amount of monomersor low molecular weight species can affect the degradation rate of apolymer. Second, if the same or similar stock is not used, new polymericcontaminants may be introduced that can affect the degradation rate ofthe polymer.

In some embodiments, the polymers include, but are not limited to,poly(dioxanone) and poly(ethylene oxide)/poly(lactic acid);poly(anhydrides), poly(alkylene oxalates); poly(phosphazenes);poly(urethanes); silicones; poly(esters; poly(olefins); copolymers ofpoly(isobutylene); copolymers of ethylene-alphaolefin; vinyl halidepolymers and copolymers such as poly(vinyl chloride); poly(vinyl ethers)such as, for example, poly(vinyl methyl ether); poly(vinylidene halides)such as, for example, poly(vinylidene chloride); poly(acrylonitrile);poly(vinyl ketones); poly(vinyl aromatics) such as poly(styrene);poly(vinyl esters) such as poly(vinyl acetate); copolymers of vinylmonomers and olefins such as poly(ethylene-co-vinyl alcohol) (EVAL),copolymers of acrylonitrile-styrene, ABS resins, and copolymers ofethylene-vinyl acetate; and any derivatives, analogs, homologues,congeners, salts, copolymers and combinations thereof.

In some embodiments, the polymers include, but are not limited to,poly(amides) such as Nylon 66 and poly(caprolactam); alkyd resins;poly(carbonates); poly(oxymethylenes); poly(imides); poly(ester amides);poly(ethers) including poly(alkylene glycols) such as, for example,poly(ethylene glycol) and poly(propylene glycol); epoxy resins;polyurethanes; rayon; rayon-triacetate; biomolecules such as, forexample, fibrin, fibrinogen, starch, poly(amino acids); peptides,proteins, gelatin, chondroitin sulfate, dermatan sulfate (a copolymer ofD-glucuronic acid or L-iduronic acid and N-acetyl-D-galactosamine),collagen, hyaluronic acid, and glycosaminoglycans; other polysaccharidessuch as, for example, poly(N-acetylglucosamine), chitin, chitosan,cellulose, cellulose acetate, cellulose butyrate, cellulose acetatebutyrate, cellophane, cellulose nitrate, cellulose propionate, celluloseethers, and carboxymethylcellulose; and any derivatives, analogs,homologues, congeners, salts, copolymers and combinations thereof.

In some embodiments, at least one of polymers can be a poly(esteramide), a poly(lactide) or a poly(lactide-co-glycolide) copolymer; andany derivatives, analogs, homologues, congeners, salts, copolymers andcombinations thereof.

In some embodiments, the polymers can be biodegradable, bioerodableand/or bioabsorbable. Examples of biodegradable polymers include, butare not limited to, polymers having repeating units such as, forexample, an a-hydroxycarboxylic acid, a cyclic diester of an.alpha.-hydroxycarboxylic acid, a dioxanone, a lactone, a cycliccarbonate, a cyclic oxalate, an epoxide, a glycol, an anhydride, alactic acid, a glycolic acid, a lactide, a glycolide, an ethylene oxide,an ethylene glycol, and any derivatives, analogs, homologues, congeners,salts, copolymers and combinations thereof.

In some embodiments, the biodegradable polymers include, but are notlimited to, polyesters, poly(ester amides); poly(hydroxyalkanoates)(PHA), amino acids; PEG and/or alcohol groups; polycaprolactones,poly(D-lactide), poly(L-lactide), poly(D,L-lactide), poly(meso-lactide),poly(L-lactide-co-meso-lactide), poly(D-lactide-co-meso-lactide),poly(D, L-lactide-co-meso-lactide), poly(D,L-lactide-co-PEG) blockcopolymers, poly(D,L-lactide-co-trimethylene carbonate), polyglycolides,poly(lactide-co-glycolide), polydioxanones, polyorthoesters,polyanhydrides, poly(glycolic acid-co-trimethylene carbonate),polyphosphoesters, polyphosphoester urethanes, poly(amino acids),polycyanoacrylates, poly(trimethylene carbonate), poly(imino carbonate),polycarbonates, polyurethanes, copoly(ether-esters) (e.g. PEO/PLA),polyalkylene oxalates, polyphosphazenes, PHA-PEG, and any derivatives,analogs, homologues, salts, copolymers and combinations thereof.

In other embodiments, the polymers can be poly(glycerol sebacate);tyrosine-derived polycarbonates containing desaminotyrosyl-tyrosinealkyl esters such as, for example, desaminotyrosyl-tyrosine ethyl ester(poly(DTE carbonate)); and any derivatives, analogs, homologues, salts,copolymers and combinations thereof.

In some embodiments, the polymers are selected such that theyspecifically exclude any one or any combination of any of the polymerstaught herein.

In the manufacturing process using device 50, 70, 80, a polymeric tube58, 78, 88 may be placed on support member 52, 72, 82 with the polymericmandrel 54, 74, 84 being placed inside polymer tube 58, 78, 88. Thepolymeric tube 58, 78, 88 may typically be between twenty to two-hundredmillimeters long depending on its intended therapeutic application.Additionally, the inner and outer diameters of polymeric tube 58, 78, 88may vary in accordance with the intended therapeutic application and inaccordance with the outer diameter of mandrel 54, 74, 84. In someembodiments, the ID of polymeric tube 58, 78, 88 may approximately thesame as the OD of polymeric mandrel 54, 74, 84. In one embodiment,polymer mandrels may range in size from 0.01″ OD to 0.14″ OD, withcorresponding polymeric tubing ranging from 0.04″ ID to 0.15″ ID. In anembodiment, polymeric tube 58, 78, 88 is of a size between 0.07″ ID and0.13″ ID, and a corresponding polymer mandrel 54, 74, 84 in the range of0.04″ OD to 0.08″ OD.

In certain embodiments of the invention, if the OD of polymeric mandrel54, 74 is too large, it may interfere with second support 51, 71. Also,if the OD of polymeric mandrel 54, 74, 84 is smaller than 0.01″, thenpolymeric mandrel 54, 74, 84 may not provide adequate shielding duringthe laser cutting process. The polymeric mandrel 54, 74, 84 must be wideenough in diameter with respect to the diameter of the laser beam 100 toprevent a portion of the beam from hitting an unshielded portion of thepolymeric tube 58, 78, 88. In order for polymeric mandrel 54, 74, 84 tofreely roll in polymeric tube 58, 78, 88, the OD of polymeric mandrel54, 74, 84 must be smaller than the ID of polymeric tube 58, 78, 88.

The polymeric mandrels may be solid rods with a smooth or rough outsidesurface. A solid rod does not contain a hollow portion between thecentral longitudinal axis and the outside diameter of the rod. If therod contains a hollow portion between the central longitudinal axis andthe outside diameter of the rod, it is considered a hollow rod. Inanother embodiment the polymeric mandrels are hollow with the outsidesurfaces being smooth or rough. Additionally, if polishing of the innersurface of the generally tubular polymeric member is desired, a smoothouter surface polymeric mandrel is generally preferred.

The generally tubular polymeric member from which the polymeric stent iscut is expanded, extruded tubing. The fabrication of the polymeric stentincludes radially expanding an extruded polymeric tube about itscylindrical axis. Radial expansion deforms the tube circumferentiallywhich increases the radial strength of the polymeric tubing, and thesubsequently a stent fabricated from the expanded tube. The radialexpansion of the polymer tube can be accomplished by a blow moldingprocess. In such a process, the polymer tube is disposed within acylindrical mold with a diameter greater than the polymer tube. Thepolymer tube is heated. The pressure inside of the tube is increased byblowing a gas into the tube to cause radial expansion of the tube so theoutside surface of the tube conforms to the inside surface of the mold.The polymer tube can be axially deformed by a tensile force along thetube axis before, during, and/or after the radial deformation. In someinstances, only sufficient tension is applied to maintain the length ofthe tube as it is expanded. The polymer tube is then cooled below Tg andfurther processing steps can then be performed, such as laser machiningof the tube to form a stent pattern.

The polymeric mandrel may be made from the same stock tubing as thegenerally tubular polymeric member by expanding each tube to a differentdiameter. In an embodiment, the polymeric mandrel is expanded to asmaller diameter than the generally tubular polymeric member.

A laser 100 may be used for the etching process when forming a polymericstent 10 from polymeric tube 8 in FIG. 1. The laser 100 may be used in arange of fifty milliwatts to one watt, depending on the environmentalconditions surrounding the laser. A typical lasing process to completean entire stent takes approximately two minutes to twelve minutes, moreparticularly approximately six minutes, pursuant to a method of thisinvention.

One of skill in the art will realize that the strength of the laser andthe thickness of the polymeric mandrel should be adjusted so that thelaser cuts through the polymeric tube and either degrades the surface ofthe polymeric mandrel or cuts through the mandrel if it is hollow. Inone embodiment, the polymeric mandrel is hollow of a thickness thatallows the laser to penetrate one side of the polymeric mandrel, withoutgoing entirely through the polymeric mandrel. Polymeric mandrels withthinner walls are preferred because they are lighter and arepreferentially worn away by the laser before the polymeric tube. Asshown in FIG. 8D, if a solid polymeric mandrel 84 is used, or the wallsare too thick on the polymeric mandrel 84, the laser beam 101 from laser100 may scatter material as well as energy 102 instead of absorbing theenergy, possibly resulting in damage 103 to the inner surface ofpolymeric tube 88.

In FIG. 9, a polymeric stent 10 manufactured in accordance with device50, 70, 80 is illustrated. As discussed previously, the polymeric stent10 can include a plurality of struts 12 linked by connecting elements14, with gaps 16 positioned between the struts and the connectingelements. The polymeric stent 10 can also include a proximal ring 18, adistal ring 20 and at least one central ring 22. Generally, thepolymeric stent 10 is a bioerodable, biodegradable or bioabsorbableimplantable medical device that is intended to remain in the body untilits intended function is achieved.

In FIGS. 10 and 11, cross-sectional and enlarged views of the polymerstent of FIG. 9 are illustrated, respectively. Generally absent from theinner surface 26 is at least one angled cut 28. This is substantiallydue to the polymeric mandrel 54, 74, 84, which provides a shieldingeffect to the inner surface when the equal-but-opposite outer surface isbeing lased during the manufacturing process. Moreover, becausepolymeric mandrel 54, 74, 84 is composed of a biocompatible polymer, theproblems of undesirable residual contaminants left by typical glass ormetal mandrels, for example, are substantially reduced or completelyeliminated. In one embodiment, the working polymeric tube issubstantially free of metal and glass. In an embodiment the polymericmandrel is substantially free of metal and glass.

In a further embodiment, the mandrel may be designed to absorb any laserlight that leaks through from the cutting process. The mandrel may bemanufactured by adding a pigment or a dye to the polymeric materialduring the extrusion process, or by placing a second mandrel inside ofthe hollow polymer mandrel. In an embodiments, the second mandrel isconstructed of a metallic material, or a material that can stronglyabsorb light. This would assist in preventing the scattering of lightillustrated in FIG. 8D.

The polymeric stent 10 described in FIGS. 9, 10 and 11 may be coatedwith one or more therapeutic agents, including an anti-proliferative,anti-inflammatory or immune modulating, anti-migratory, anti-thromboticor other pro-healing agent or a combination thereof. Theanti-proliferative agent can be a natural proteineous agent such as acytotoxin or a synthetic molecule or other substances such asactinomycin D, or derivatives and analogs thereof (manufactured bySigma-Aldrich 1001 West Saint Paul Avenue, Milwaukee, Wis. 53233; orCOSMEGEN available from Merck) (synonyms of actinomycin D includedactinomycin, actinomycin IV, actinomycin I1, actinomycin X1, andactinomycin C1), all taxoids such as taxols, docetaxel, and paclitaxel,paclitaxel derivatives, all olimus drugs such as macrolide antibiotics,rapamycin, everolimus, structural derivatives and functional analoguesof rapamycin, structural derivatives and functional analogues ofeverolimus, FKBP-12 mediated mTOR inhibitors, biolimus, perfenidone,prodrugs thereof, co-drugs thereof, and combinations thereof.Representative rapamycin derivatives include40-O-(3-hydroxy)propyl-rapamycin,40-O-[2-(2-hydroxy)ethoxy]ethyl-rapamycin, or 40-O-tetrazole-rapamycin,40-epi-(N1-tetrazolyl)-rapamycin (ABT-578 manufactured by AbbotLaboratories, Abbot Park, Ill.), prodrugs thereof, co-drugs thereof, andcombinations thereof.

The coating method may be applied by a variety of methods, such as thosedisclosed in U.S. Pat. No. 6,818,063 to Kerrigan and U.S. Pat. No.6,695,920 to Pacetti et al. In addition, the therapeutic drug may beincorporated within the polymeric tube 8 thereof, such as disclosed inU.S. Pat. No. 5,605,696 to Eury et al. Also, the polymeric tube 8 mayinclude at least two layers of polymers with different chemicalcharacteristics for purposes of, for example, adjusting the flexibilitycharacteristic of the polymeric stent 10.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications can be made without departing from thisinvention in its broader aspects. Therefore, the appended claims are toencompass within their scope all such changes and modifications as fallwithin the true spirit and scope of this invention.

1. A method of producing a polymeric stent, comprising: positioning apolymeric mandrel and a polymeric tube relative to the other such thatthe polymeric mandrel is within the polymeric tube and in contact withthe polymeric tube inside surface, forming a tubing-mandrel assembly,wherein the polymeric mandrel rolls on the inside surface of thepolymeric tube and the polymeric tube has a first end and a second end;cutting the polymeric tube while the polymeric mandrel is positionedwithin the polymeric tube with a laser to form an implantable medicaldevice; and removing the implantable medical device from the mandrel,wherein the polymeric tube is only supported at the first end.
 2. Amethod for manufacturing a polymeric stent, comprising: providing agenerally tubular polymeric member having a working outer tube and aninner tube surface defining an inside diameter of the generally tubularpolymeric member, the generally tubular polymeric member having a firstend and a second end; providing a polymeric mandrel within the generallytubular polymeric member, the polymeric mandrel having an outer surfacedefining an outer diameter that is smaller than the inside diameter ofthe generally tubular polymeric member; supporting the generally tubularpolymeric member on only at the first end, with the polymeric mandreltherewithin, in operative association with a laser beam; impinging thelaser beam upon the working outer tube surface thereby causing the laserbeam to cut a kerf, then pass through a space between the inner tubesurface and the outer surface of the polymeric mandrel and then contactthe polymeric mandrel such that the laser beam is prevented fromcontacting the portion of the inner tube surface upon which saidpolymeric mandrel is placed; cutting a stent pattern in the generallytubular polymeric member near the second end; and removing a completedstent from the second end of the generally tubular polymeric memberthereby leaving a new second end on the generally tubular polymericmember.
 3. The method of claim 2, wherein after removing the completedstent, a new stent is cut without supporting the new second end of thegenerally tubular polymeric member.
 4. The method of claim 2, whereinthe polymeric mandrel is moved longitudinally along the inner tubesurface of the generally tubular polymeric member toward the first orsecond end.
 5. The method of claim 2, wherein the polymeric mandrelrolls around the cylindrical axis of the inner tube surface of thegenerally tubular polymeric member.
 6. The method of claim 2, whereinthe polymeric mandrel is hollow.
 7. The method of claim 2, wherein thepolymeric mandrel is a solid rod that is not hollow.
 8. The method ofclaim 2, further comprising dispensing pressurized gas through a nozzlenear the laser cutting point, thereby forming a jet of pressurized gasto force debris toward the second end of the generally tubular polymericmember.
 9. A stent cutting apparatus, comprising: a generally tubularpolymeric member having a working outer tube and an inner tube surfacedefining an inside diameter of the generally tubular polymeric member,the generally tubular polymeric member having a first end and a secondend; a polymeric mandrel having an outer surface defining an outerdiameter that is smaller than the inside diameter of the generallytubular polymeric member; a support adapted to hold the generallytubular polymeric member on at least the first end, with the polymericmandrel therewithin, in operative association with a laser beam; anozzle near the laser beam cutting point adapted to dispense pressurizedgas, thereby forming a jet of pressurized gas to force debris out of thelaser cut kerf toward the second end of the generally tubular polymericmember, wherein the polymeric mandrel is positioned longitudinallywithin the generally tubular polymeric member such that the outersurface of the polymeric mandrel is in contact with the inner tubesurface of the generally tubular polymeric member approximately at abottom of the generally tubular polymeric member due to gravity, whereinwhen the generally tubular polymeric member rotates in a direction thepolymeric mandrel rolls in the same direction in response to an angularforce from the rotation of the generally tubular polymeric member.